Feature Request: support updating/rebuilding multiple projects

I'd love for Paket to support upgrading references for multiple projects at the same time. My use case is that I have a 185 lines long paket.lock file with almost only my own packages; upgrading all of them, e.g. to ensure there are no lingering runtime "MethodMissingException", would be very pleasant.

I could envision running paket in a folder and it going through all subfolders, looking for paket.lock. If there are interdependencies between the projects in the folders, it would do a normal topological sort and start with the leafs, upgrading its dependencies, trigger a rebuild, test, version increment, release and then move on to the next subfolder/project.

I can give you access to our code if you want to see how it's all composed; it's all-F# and about 15 different libraries that I've built. In return for this feature you can choose a project that we open source; they are all built with that in mind. ;) Projects include: F# S3 API, a CQRS-framework + testing framework to name a few.

The issue names no files or tests. Start by tracing Paket's existing project upgrade flow, then assess project discovery, dependency ordering, rebuild and test execution, version increments, and release handling. Done would mean a documented, tested workflow that upgrades multiple interdependent projects in the requested order.